Molecular cloning and function analysis of FAD2 gene in Idesia polycarpa

Functional validation of ZbFAD2 and ZbFAD3 in the alkylamide biosynthesis pathway from Zanthoxylum bungeanum Maxim

The spicy taste and medicinal properties of Zanthoxylum bungeanum are imparted by several alkylamides. Although most studies have focused on their isolation and identification, few have reported their biosynthesis pathways. Among the differentially expressed genes (DEGs) reported in the numerous varieties of Z. bungeanum, some might contribute to alkylamide biosynthesis. However, they are not yet functionally validated. The present study explored the function of two genes, ZbFAD2 and ZbFAD3, in the alkylamide biosynthesis pathway, and their stable and transient expression in Arabidopsis thaliana and Nicotiana benthamiana were also analyzed. As compared with the wild-type (WT), the fatty acid content analysis indicated that ZbFAD2-A. thaliana transgenic seeds had lower oleic acid and higher linoleic acid contents, while the ZbFAD3-A. thaliana transgenic seeds showed lower linoleic acid and higher α-linolenic acid levels. Moreover, hydroxy-α-sanshool, a major alkylamide, was considerably higher in the ZbFAD2-N. benthamiana transgenic plants (0.2167 ± 0.0026 mg/g) than in the WT (0.0875 ± 0.0049 mg/g), while it was lower in the ZbFAD3-N. benthamiana transgenic plants (0.0535 ± 0.0037 mg/g). These results suggest that both ZbFAD2 and ZbFAD3 are vital alkylamide biosynthesis enzymes in Z. bungeanum. Our study not only helps to scale up the alkylamide production, but also establishes the role of the uncharacterized genes.

Transcriptome analysis provides novel insights into the soil amendments induced response in continuously cropped Codonopsis tangshen

Codonopsis tangshen Oliv (C. tangshen) is an important Chinese traditional medicinal plant with various health benefits. However, the growth of C. tangshen are seriously affected by continuous cropping, which led to the decrease of the yield and quality. A field experiment was conducted to learn the effects of soil amendments on the growth of C. tangshen under continuous cropping condition, and the biological events which occurred at molecular level were investigated. The results indicated that the content of chlorophyll a (Chl a), chlorophyll b (Chl b), and carotenoid (Car) was significantly higher in SCPM (silicon-calcium-potassium-magnesium fertilizer), SCPMA (SCPM combined with azoxystrobin) and SCPMAOM (SCPM combined with azoxystrobin and organic manure) treatments. Moreover, the yield and the levels of alkaloid, polysaccharide, flavone and total protein in the treatments of SCPM, SCPMA and SCPMAOM were significantly higher than those in the control, and these indexes were all highest in the SCPMAOM treatment. RNA-sequencing (RNA-Seq) is an economical and efficient method to obtain genetic information for species with or without available genome data. In this study, RNA-Seq was performed to understand how continuously cropped C. tangshen responded to the soil amendments at the transcriptome level. The number of differentially expressed genes (DEGs) were as follows: CK vs. SCPM (719 up- and 1456 down-), CK vs. SCPMA (1302 up- and 1748 down-), CK vs. SCPMAOM (1274 up- and 1678 down-). The soil amendments affected the growth of C. tangshen mainly by regulating the genes involved in pathways of 'photosynthesis,' 'plant hormone signal transduction,' 'biosynthesis of unsaturated fatty acids,' 'phenylpropanoid biosynthesis,' and 'starch and sucrose metabolism,' etc. qRT-PCR was performed to validate the expressions of 10 target genes such as CP26, PsaF, and POX, etc., which verified the reliability of RNA-Seq results. Overall, this study revealed the roles and underlying mechanisms of the soil amendments in regulating the growth of continuously cropped C. tangshen at transcriptome level. These findings are beneficial for improving the continuous cropping tolerance and may be valuable for future genetic improvement of C. tangshen.

Comparative Analysis and Structural Modeling of Elaeis oleifera FAD2, a Fatty Acid Desaturase Involved in Unsaturated Fatty Acid Composition of American Oil Palm

Simple Summary

Palm oil has become the world’s most important vegetable oil in terms of production quantity, and its overall demand is exponentially growing with the global population. The fatty acid composition and particularly the oleic/linoleic acid ratio are major factors influencing palm oil quality. In this study, we focused on FAD2, a fatty acid desaturase enzyme involved in the desaturation and conversion of oleic acid to linoleic acid in Elaeis oleifera, identified through in silico annotation analysis. Our phylogenetic and comparative studies revealed two SNP markers, SNP278 and SNP851, significantly correlated with the oleic/linoleic acid contents. Our study provides fundamental insights into the mechanism of fatty acids synthesis in oil palm and could support the application of molecular biology techniques to enhance the enzymatic activity and substrate affinity of EoFAD2.

Abstract

American oil palm (Elaeis oleifera) is an important source of dietary oil that could fulfill the increasing worldwide demand for cooking oil. Therefore, improving its production is crucial and could be realized through breeding and genetic engineering approaches aiming to obtain high-yielding varieties with improved oil content and quality. The fatty acid composition and particularly the oleic/linoleic acid ratio are major factors influencing oil quality. Our work focused on a fatty acid desaturase (FAD) enzyme involved in the desaturation and conversion of oleic acid to linoleic acid. Following the in silico identification and annotation of Elaeis oleifera FAD2, its molecular and structural features characterization was performed to better understand the mechanistic bases of its enzymatic activity. EoFAD2 is 1173 nucleotides long and encodes a protein of 390 amino acids that shares similarities with other FADs. Interestingly, the phylogenetic study showed three distinguished groups where EoFAD2 clustered among monocotyledonous taxa. EoFAD2 is a membrane-bound protein with five transmembrane domains presumably located in the endoplasmic reticulum. The homodimer organization model of EoFAD2 enzyme and substrates and respective substrate-binding residues were predicted and described. Moreover, the comparison between 24 FAD2 sequences from different species generated two interesting single-nucleotide polymorphisms (SNPs) associated with the oleic/linoleic acid contents.

Characterization of genes encoding ω-6 desaturase PoFAD2 and PoFAD6, and ω-3 desaturase PoFAD3 for ALA accumulation in developing seeds of oil crop Paeonia ostii var. lishizhenii

Paeonia ostii var. lishizhenii has emerged as a valuable oil-producing crop with splendid characteristic of high α-linolenic acid (C18:3, ALA) content in its seed oil for healthy food supplement, but the molecular mechanism for seed ALA accumulation remains enigmatic. In our previous report, a PoSAD gene encoding stearoyl-ACP desaturase had been cloned and functional charactered for the first desaturation procedure involved in ALA biosynthesis pathway in P. ostii var. lishizhenii endosperms, while other participants have not been identified to date. In this study, full-length cDNAs of PoFAD2 (1489 bp), PoFAD6 (1638 bp), and PoFAD3 (1709 bp) were isolated based on our recent transcriptome sequencing data. Bioinformatic analyses revealed that the PoFADs were closest to their counterparts from Paeoniaceae species P. ludlowii, P. rockii, and P. suffruticosa in phylogenetic tree, which shared highly conserved histidine boxes (HXXXH, HXXHH, and HXXHH), exhibiting typical characters of membrane-bound desaturases in higher plants. Additionally, the PoFAD2 and PoFAD3 were specifically expressed and highly associated with LA and ALA accumulation in developing endosperms, whereas PoFAD6 expression has no significantly difference during whole seed developing stages. The catalytic function of these PoFADs were further analyzed by heterologous expression in Saccharomyces cerevisiae and Arabidopsis thaliana. The results showed that PoFAD2 and PoFAD6 could catalyze linoleic acid (C18:2) synthesis, while PoFAD3 had ability to produce ALA. This study functional identified three PoFAD genes, which indicates their critical roles in ALA biosynthesis pathway in P. ostii var. lishizhenii, and is of great theoretical and practical meaning on breeding and cultivating new tree peony varieties to promote human health and nutrition supplement.

Linum usitatissimum FAD2A and FAD3A enhance seed polyunsaturated fatty acid accumulation and seedling cold tolerance in Arabidopsis thaliana

Flax (Linum usitatissimum) seed oil is rich in polyunsaturated fatty acids (PUFAs), particularly linolenic acid, which is converted from linoleic acid. Studies have indicated that the biosynthesis of linoleic acid and linolenic acid is controlled by FAD2 and FAD3, respectively. However, the functional distinctions of different LuFAD2 and LuFAD3 copies from L. usitatissimum in governing the biosynthesis of linoleic acid or linolenic acid, respectively, remain unclear. In this study, five LuFAD2 and three LuFAD3 cDNAs were cloned from the L. usitatissimum cultivar 'Longya 10', and GC-MS results demonstrated that LuFAD2A and LuFAD3A play predominant roles in the accumulation of linoleic acid and linolenic acid, respectively. Their simultaneous overexpression in Arabidopsis thaliana seeds led to a significant increase in fatty acid contents, especially PUFAs. Additionally, LuFAD2A and LuFAD3A promoted the biosynthesis of jasmonic acid by increasing the levels of linolenic acid, which, in turn, enhanced plant cold tolerance. When the amount of linolenic acid is not sufficient, plants adapt to low temperature via the accumulation of anthocyanins. These findings provide insights into the higher accumulation of PUFAs in L. usitatissimum seeds, and provide potential targets for improving oil quality of other oil-producing crops through molecular manipulation.

Functional characterization and expression profile of microsomal FAD2 and FAD3 genes involved in linoleic and α-linolenic acid production in Leucas cephalotes

The genus Leucas belongs to Lamiaceae, and has attained more attention due to the presence of unusual allenic fatty acids called laballenic and phlomic acid in majority of its species. This genus has been known since traditional medicinal times and has numerous economical, nutritional, and industrial properties. So far genetic, molecular and biochemical analyses of lipid metabolism and fatty acid biosynthetic pathway in Leucas has not been reported. The objective of this study is to identify, isolate, analyze expression profiles, and functionally characterize the membrane-associated desaturases responsible for unsaturated fatty acid accumulation in Leucas cephalotes. Full-length LcFAD2 and LcFAD3 cDNAs were isolated and expressed in Saccharomyces cerevisiae BY4741 for functional characterization. Substrate feeding assay using S. cerevisiae confirmed that the LcFAD2 enzyme catalyzes desaturation of both palmitoleic (16:1∆⁹) and oleic (18:1∆⁹) acids to form palmitolinoleic (16:2∆^9,12) and linoleic (18:2∆^9,12) acids respectively. As a contrast, the heterologous activity of LcFAD2 enzyme in S. cerevisiae led to the synthesis of palmitolinoleic (16:2∆^9,12) acid, an unusual fatty acid that is not found naturally in Leucas cephalotes. While the LcFAD3 enzyme catalyzed linoleic acid (18:2∆^9,12) into α-linolenic acid (18:3∆^9,12,15). Furthermore, transcript abundance of LcFAD2 and LcFAD3 cDNAs were estimated from various plant parts such as roots, shoots, leaves, petals and developing seeds. Our results have shown that the differential transcriptional activity of LcFAD2 and LcFAD3 desaturase genes differs significantly in developing seeds, petals, leaves, stems, and roots of L. cephalotes. Furthermore, for the industrial production of these essential fatty acids, namely, linoleic and α-linolenic acid, FAD2 and FAD3 enzyme activity could be exploited from this upcoming significant oil plant, Leucas cephalotes.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01016-z.

Characterization of diacylglycerol acyltransferase 2 from Idesia polycarpa and function analysis

Idesia polycarpa is an oil-producing tree native to China and Northeast Asia. The fruits of I. polycarpa which are named oil grape are unique in that they contain large amounts saturated and unsaturated lipids. Diacylglycerol acyltransferase 2 (DGAT2) is a key enzyme catalyzing the final step of triacylglyceride (TAG) synthesis. However, expression and bioinformatics of DGAT2 in I. polycarpa are still blank. In order to further understand the lipogenesis of oil grape, we contrasted seven various growth periods fruits from seed formation to seed maturation. Lipid accumulation rates and final lipid content were significantly different among the different periods. We cloned and characterized the DGAT2 gene from fruits of I. polycarpa. A partial fragment of 239 bp of IpDGAT2 was amplified by PCR. We cloned the open-reading frame (ORF) of IpDGAT2 by RACE technique. The ORF of IpDGAT2 contains 984 bp and encodes 327 amino acids. The qPCR analysis manifested that IpDGAT2 was expressed in all oil grape growing periods and expression was highest on September 20 (seed maturation). In I. polycarpa fruits the expression of IpDGAT2 was positively correlated with the lipid accumulation rates. Rhodotorula glutinis expression analysis showed that IpDGAT2 have a diacylglycerol acyltransferase bio-functional. Heterologous expression of the 35S::IpDGAT2 in Arabidopsis thaliana confirmed that the isolated IpDGAT2 could catalyze lipid synthesis. The lipid content increased by 40 % in transgenic plants relative to the control. which suggests that high lipid content fruits can be created by the overexpression of IpDGAT2 in I. polycarpa.

Characterization of the stearoyl-ACP desaturase gene (PoSAD) from woody oil crop Paeonia ostii var. lishizhenii in oleic acid biosynthesis

Paeonia ostii var. lishizhenii has been approved as a woody oil crop with the outstanding characteristic of abundant α-linolenic acid (C18:3, ALA) in its seed oil. The stearoyl-ACP desaturase gene (SAD) regulates the first key step from stearic acid (C18:0, SA) to oleic acid (C18:1, OA) in the ALA biosynthetic pathway, but its functional characterization in P. ostii var. lishizhenii is absent to date. In this study, a key PoSAD gene (1719 bp in length) was acquired from endosperm of P. ostii var. lishizhenii by transcriptome sequencing analysis and the RACE (rapid-amplification of cDNA ends) method. Bioinformatic analysis of the PoSAD protein showed high homology (ranging from 90.4% to 94.4%) and similar physical and chemical properties to SAD from other higher plants, indicating that it encodes a putative stearoyl-ACP desaturase. Analysis of cis-acting elements found several endosperm tissue-specific motifs; i.e., one Prolamin box, thirteen DOFCOREs and one RY repeat in its promoter. The results of the qRT-PCR experiments verified that PoSAD was most highly expressed in developing endosperm at 59 days after pollination (53.7 times that in shoots) compared with that in roots (1.4 times), stems (2.5 times), leaves (3.1 times), petals (13.1 times) and stamens (46.0 times). Meanwhile, the fatty acid contents in P. ostii var. lishizhenii endosperm at seven growth stages were compared with variation in PoSAD expression. Heterologous expression of PoSAD significantly decreased SA and increased OA content, which effectively reduced the ratios of SA to OA in Saccharomyces cerevisiae and Arabidopsis thaliana. However, contents and ratios of palmitic acid (C16:0) and palmitoleic acid (C16:1) were stable in transgenic yeast, and palmitoleic acid remained absent in transgenic A. thaliana seeds. These results illustrate that PoSAD plays an essential role in endosperm development of P. ostii var. lishizhenii, strictly in catalysis of SA desaturation and OA biosynthesis but without functioning in PA desaturation. The results contribute to our understanding of the characterization of PoSAD in OA biosynthesis in P. ostii var. lishizhenii.